1. Field of the Invention
The present invention relates to a drive chain for use in a bicycle, and more particular to a drive chain used for a bicycle having a change speed apparatus.
2. Description of the Related Arts
A conventional bicycle drive chain of the above-noted type includes a first plate and a second plate each having connecting portions at its opposed ends. These first and second plates are alternately connected with each other through the respective connecting portions with one plate positioned outwardly of the other in the direction of plate thickness. When such drive chain is moved from one gear to another of a multi-gear assembly of the change-speed apparatus, the engagement onto the new gear usually starts between a wide gear hole formed by the second plate positioned outwardly in the transverse direction of the chain and one gear tooth and then is followed in succession by the next gear holes of the chain and the next teeth of the gear, thereby to complete the engagement. In the above, in many cases, the engagement does not start between a narrow hole of the chain and the gear tooth. Then, one conceivable way to improve the width wise engageability of the chain is to further widen the wide gear hole, as suggested e.g. by a Japanese published utility model No. 55-1988, which drive chain is illustrated in FIG. 9. According to this drive chain, a middle portion forming the wide gear hole and positioned between the opposed connecting portions of the second plate is deformed outwardly in the plate thickness direction relative to the connecting portions, such that this second plate can form an even wider gear hole.
On the other hand, there is also known a conventional drive chain commonly referred to as an offset type drive chain. In this offset type, each of the first plate and the second plate has a stepped portion in a middle position thereof so as to allow a first connecting portion of one plate to be positioned outwardly of a second connecting portion of the other plate in the transverse direction of the chain. Then, a plurality of these plate pairs are alternately connected with each :other via pins with a narrow connecting portion of one plate being positioned inwardly of a wide connecting portion of the other plate in an overlapped manner.
With the above-described drive chain of the Japanese utility model publication No. 55-1988, the improvement of the gear-engageability of the chain is attempted merely by further increasing the width of the wide gear hole formed in between an opposing pair of second plates. Therefore, the chain gear engagement opportunity is still limited to that between the wide hole and the gear teeth, with no improvement being made in the engagement opportunity of the narrow gear holes. Further, with this prior construction, when there occurs a significant displacement between the hole line of the chain and the teeth line of the gear for a change-speed operation, the chain often fails to engage with the gear and slips off the same. Describing more particularly, such chain-gear displacement usually occurs when the chain line deflectes at one of its wide hole from the gear teeth line, which condition is illustrated in FIG. 9. In this FIG. 9, the moving direction of the gear teeth is denoted by an arrow. In this condition, a pair of leftside first and second plates Al and B1 are properly engaged with the gear teeth whereas the next second plate B2 forming the following wide gear hole b1 is displaced from 1 he center of the gear teeth line. Accordingly, the inner wall of the first plate A2 forming the rightmost narrow gear hole a2 rides on the top edge of corresponding gear tooth, thereby interferring with the proper chain gear engagement. Then, any effective means to overcome this problem has not been provided in the aforementioned offset type drive chain either.
In view of the above described state of the art, the primary object of the present invention is to overcome the above problem of the prior art by providing an improved drive chain which permits proper chain-gear engagement from either of the gear holes formed by the first and second plates and which can effectively prevent such riding of a plate on a gear tooth even if the chain line is deflected from the center of a gear teeth line.